Given I have an alpha blank/white, and two substituted black/black sigs, I'd discourage black/black or white/white or transparent/transparent.

I do find the clash visually, even to other people when they see the transition of black white very distracting. I wear my b/w alpha on my thumb and if it happens to slip around from its usable position, which is basically chip side down inner and other thumb edge, The transparent looks good, with the black being very constrasting/distracting - more so that the silver on my alpha.

I agree that Transparent/Black is too contrasting.
Transparent/Transparent wouldn't allow to distinguish chips without taking off the ring to check the laser branding..
so Transparent/White is the option to go for IMHO..

Transparent! I love what I'm seeing. And since there'll be two tags, I don't really mind the color of the second one.
I thing white/transparent would be cool, because it'd be hard to tell the white tag it's there, but even if you go with transparent/black, one that doesn't like the contrast could wear it transparent side up.
Same color on both sides could make things a bit unpredictable for some of us. My ring keeps turning through out the day and if I couldn't tell the two sides apart and was actually using this one to store pins or passwords, that'd be a problem.